Adsorption Desorption Behavior of Water Soluble Film Persistent Corrosion Inhibitor
- Sunder Ramachandran (Baker Hughes, a GE company) | Carlos Menendez (Baker Hughes, a GE company) | Lei Huang (Baker Hughes, a GE company) | Zhengwei Liu (Baker Hughes, a GE company) | Jimmy Ott (Baker Hughes, a GE company)
- Document ID
- NACE International
- CORROSION 2019, 24-28 March, Nashville, Tennessee, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. NACE International
- Corrosion Inhibitor Availability, Batch Treatment, CO2 Corrosion, Desorption, Corrosion Inhibition, Adsorption
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- 22 since 2007
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Water based corrosion inhibitors that provide longer treatment lives and better protection than similar inhibitors in oil-based formulations were recently developed. Conventional film persistency tests on these inhibitors allow comparative evaluation of different corrosion inhibitors. Langmuir adsorption and desorption has been recently used to form a method of evaluating the impact of the loss of availability of a corrosion inhibitor. The adsorption-desorption analysis allowed quantitative assessment of loss of availability. In this paper, a water-soluble corrosion inhibitor characterized as film persistent in conventional laboratory tests and field experience is studied. The values of adsorption and desorption will be compared with values with a corrosion inhibitor that is not used in batch treatments. The work will aid quantitative laboratory assessment of film persistency.
In earlier work, the adsorption desorption behavior of corrosion inhibitor performance was interpreted using Langmuir adsorption to obtain information on the film persistence of a continuous corrosion inhibitor used in the given field.1 In this paper the same technique will be applied to corrosion inhibitors that have greater film persistence. The use of Langmuir adsorption is appropriate for non-scaling environments. In many instances, CO2 corrosion is associated with iron carbide or iron carbonate on the surface.2 Complications occur due to scale precipitation alongside inhibitor adsorption and desorption. The brine used in the previous work contains both acetic acid and calcium. Previous work has indicated that there is no significant effect of acetic acid on iron carbonate scale formation and protectiveness.3 The apparent solubility of siderite increases with calcium ions in solution.4 The tendency for scale formation will be enhanced at higher temperatures and as iron concentrations increase. It is found in this work that there are instances where Langmuir adsorption and desorption is applicable and other instances where inhibitor adsorption and desorption occurs with scale precipitation.
Corrosion inhibitor performance was measured using kettle tests as in earlier work.1 A slight modification was introduced to the earlier procedure involving the use of a glass sleeve around the linear polarization electrode probe that prevented the working electrode from contact with the hydrocarbon phase.1 Reference and counter electrodes are made from UNS N10276. The working electrode is made from carbon steel 1018. Corrosion rates were measured using linear polarization resistance (LPR). 700 mL of brine are used in the test. The test solution is deoxygenated using a 1-hour sparge with CO2 at a flow rate of CO2 of 1.0 standard litres of CO2 per minute. Aluminum oxide bead blasted electrodes were used in this study. When the desired temperature is attained, the electrodes are inserted in the solution, then all electrode connections are made for corrosion rate monitoring. The hydrocarbon has been pre-sparged overnight with carbon dioxide to remove oxygen. Next, 300 mL of deoxygenated hydrocarbon is added to the brine. In the test, the volume fraction of brine was 70% and the hydrocarbon fraction was 30%. The blank corrosion rate is monitored for two hours. LPR measurements are conducted using a potentiostat. The test method involves measurement of the open circuit potential, and the working electrode is polarized ±5 mV from the open circuit potential. A scan rate of 0.3 mV/s is used during the polarization measurement. The working electrode of the kettle test has an area of 9 cm2. In the tests reported here, a corrosion inhibitor at 20 ppm (v/v) based on total liquid volume is injected in the solution. After24 hours testing, the probe is transferred to a fresh uninhibited solution which also contained 700 mL synthetic brine and 300mL hydrocarbon. This tests the film persistency of the chemical. A condenser is used to keep the acetates in solution.
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